Infection with the Kaposi's sarcoma associated herpesvirus (KSHV) has been linked to the occurrence of Kaposi's sarcoma (KS) and several lymphoproliferative disorders, such as primary effusion lymphoma (PEL), multicentric Castleman's disease and immunoblastic/plasmablastic lymphomas. Due to underlying immunosuppression, KSHV-associated cancers have extremely poor prognosis when treated with conventional chemotherapy and there is urgent need for more effective and less toxic therapies for these disorders. Previous studies from our laboratory have shown that KSHV-encoded viral FLICE inhibitory protein (vFLIP) K13 is a powerful activator of the NF-kB pathway and plays a key role in the pathogenesis of KSHV-associated malignancies. K13 activates the NF-kB pathway by directly interacting with the NEMO/IKK3 subunit of the IkB kinase (IKK) complex and utilizes this pathway to promote cellular survival, proliferation, transformation and cytokine secretion. The above studies have established NF-kB pathway as an important therapeutic target for the treatment of KSHV-associated malignancies. However, since NF-kB pathway plays a key role in normal immune and inflammatory responses, global inhibitors of this pathway are likely to lead to severe immunosuppression, thus limiting their potential clinical utility in KSHV-infected patients. The overall goal of this proposal is to design cell-permeable helical peptides capable of blocking K13-NEMO interaction and to test their ability to block K13-induced NF-kB using in vitro and in vivo models developed in our laboratory. It is hoped that such peptides will specifically block K13-induced NF-kB without interfering with the physiological activation of this pathway during normal immune and inflammatory response.